1. Field of the Invention
This invention relates to novel thioether furan nitrone compounds and their use as therapeutic agents and analytical reagents. More particularly, this invention concerns novel thioether furan nitrone compounds and their use as therapeutics for treating and/or preventing neurological, autoimmune and inflammatory conditions in mammals and as analytical reagents for detecting free radicals.
2. State of the Art
Alzheimer's disease is a neurodegenerative condition in which nerve cells in the brain are systematically destroyed resulting in progressive memory loss, mental confusion and ultimately death. The National Institute on Aging (NIA) has recently estimated that about 4 million people in the United States are currently afflicted with Alzheimer's disease. At present, there is no treatment that effectively prevents the disease or reverses its symptoms.
In recent years, significant progress has been made in understanding the pathogenesis of Alzheimer's disease. For example, it is now known that patients with Alzheimer's disease develop amyloid plaque deposits around and between the nerve cells of their brain. These plaque deposits are made up of fibrillar aggregates of a small peptide called amyloid .beta.-peptide or A.beta.. The plaque deposits initially form in the hippocampus and cortical regions of the brain (areas associated with memory and cognition) and then spread to other areas as the disease progresses. The deposition of fibrils and plaques is also followed by inflammation of the surrounding support cells, called glia, which may lead to further loss of neurons. The nerve cells in the brains of most Alzheimer's patients also develop tangles of a microtubule-associated protein, called tau, which are believed to be a response by the nerve cells to damage.
Progress in understanding the underlying mechanisms of Alzheimer's disease has led to the development of various in vitro and in vivo models to identify compounds effective for preventing and/or treating Alzheimer's disease and other neurodegenerative conditions. In one such in vitro model, compounds are evaluated for their ability to intervene in A.beta.(1-40) or A.beta.(1-42) beta-pleated sheet formation. Since the deposition of amyloid .beta.-peptide is associated with the development of Alzheimer's disease, compounds which effectively disrupt the formation of A.beta.(1-40) beta-pleated sheets are potentially useful for preventing and/or reversing Alzheimer's disease-related amyloid deposits.
In another in vitro model, compounds are evaluated for their ability to protect against A.beta.(25-35)-induced neuronal cell loss in rat embryonic hippocampal neuronallastrocyte cultures. As discussed above, patients with Alzheimer's disease suffer a progressive loss of neuronal cells. Accordingly, compounds which are effective in this in vitro test are potentially useful for reducing or preventing neuronal cell loss in patients afflicted with Alzheimer's disease or other neurodegenerative conditions.
A third in vitro Alzheimer's disease model is based on the observation that .beta.-amyloid increases the release of cytokines, such as interleukin-1.beta. (IL-1.beta.), interleukin 6 (IL-6) and tumor necrosis factor-.alpha. (TNF.alpha.), in human monocyte cells induced with lipopolysaccharide (LPS). IL-1.beta., IL-6 and TNF.alpha. are proteins associated with inflammatory and immune responses. As previously mentioned, the deposition of fibrils in the brains of Alzheimer's patients is associated with inflammation of the surrounding support cells. See, S. D. Yan et al., Proc. Natl. Acad. Sci. USA, 94, 5296 (1997). Thus, compounds effective in this in vitro test are potentially useful for reducing and/or preventing the inflammation associated with Alzheimer's disease.
Additionally, elevated levels of IL-1.beta., IL-6, TNF.alpha. and other cytokines are associated with a wide variety of inflammatory and autoimmune conditions, including septic shock, rheumatoid arthritis, erythema nodosum leprosy, meningococcal meningitis, multiple sclerosis, systemic lupus and the like. See, L. Sekut et al., Drug News Perspect. 1196, 9, 261; and A. Waage et al., J. Exp. Med. 1989, 170, 1859-1867. Accordingly, compounds which inhibit the production of such cytokines are potentially useful for treating such inflammatory and autoimmune conditions.
Thus, in another in vitro model, compounds are evaluated for their ability to reduce cytokine-induced neuronal cell damage in rat embryonic cortical cell cultures. As discussed above, cytokines are associated with a wide variety of inflammatory and autoimmune conditions. Accordingly, compounds which are effective in this in vitro test are potentially useful for reducing or preventing inflammatory or autoimmune conditions.
It has now been discovered that certain novel thioether furan nitrone compounds effectively inhibit the formation of A.beta.(1-42) beta-pleated sheets and/or inhibit the release of cytokines, such as IL-1.beta. and/or reduce cytokine-induced neuronal cell damage. Accordingly, such compounds are useful for the prevention and/or treatment of neurodegenerative, autoimmune and inflammatory conditions in mammals.
The thioether furan nitrone compounds of this invention are also useful as analytical reagents for detecting free radicals. In this regard, the compounds of this invention function as "spin traps" by reacting with unstable free radicals to form relatively stable free radical spin adducts which are observable by electron spin resonance (ESR) spectroscopy. Accordingly, when used as spin traps, the compounds of this invention allow free radicals to be identified and studied using ESR and related techniques.